1. Field of the Invention
This invention relates to an information distribution system. More specifically, this invention relates to such a system wherein, with the use of only a single transmitting medium, such as a first transmitting carrier frequency, and a single receiving medium, such as a second indifferent receiving carrier frequency, it is possible to service a plurality of outlying stations with a unique and private circuit for any such station.
2. Description of the Prior Art
In one application it is often necessary to provide telephone service to subscribers who are geographically located at points sufficiently remote from a Community Dial Office (CDO) so that the installation of cable for this purpose alone is impractical or not economically feasible. In such cases, telephone service is sometimes provided by radio links from the CDO to the subscribers. If a single frequency non-multiplexed system is used to service a plurality of subscribers, then only one subscriber can use the system at any time. In addition, there is a lack of privacy under these conditions. To overcome these disadvantages, systems are sometimes provided wherein each subscriber station has its own transmitting carrier frequency and (a different) receiving carrier frequency. In this way, it is possible for the base station to service more than one subscriber at a time, and each subscriber loop has privacy relative to the other subscriber loops. Another way to accomplish this end is to use this technique in combination with frequency division multiplex systems.
However, with the second described system, the central station must have as a separate receiver for each outlying station frequency (each subscriber loop), so that the cost of equipment is high, and the use of a plurality of frequencies imposes additional pressures on already overloaded frequency bands. In the version of the systems using a combination of frequency division multiplexing of a transmitted carrier from the central office, some economy of frequencies is achieved but each outlying station must be assigned one frequency division multiplex channel and one return radio frequency so that possibilities of random access still does not exist and utilization of any individual frequency or portion of the scarce radio frequency spectrum is very poor.